Operators the Sewol ferry continued to run services on the vessel even after they became aware of a critical engine failure, which could have contributed to the ship’s capsizing in April 2014, a news report said Tuesday.

An engine failure was detected in the ferry at least six months before the accident and its operator Chonghaejin Marine Co. was aware of the associated safety risks, local media outlet Media Today reported, citing company documents. But the firm was unable to find its cause or repair it.

The Sewol sinking is the country’s worst maritime disasters in history. The 6,800-ton ferry was carrying 476 passengers when it sank off the southwestern coast near Jindo on April 16, 2014, killing 304 aboard, most of whom were high school students on a field trip to Jeju Island. 

“There was an accident in which the ferry’s engine suddenly stopped working after oil steam was generated and pressure was reduced, which could have resulted in severe casualties,” Chonghaejin said in a report to the Incheon branch of the Korea Shipping Association on Sep. 26, 2013.

The ship operator requested the industry lobby to launch a probe into an excessive inflow of sludge -- a mixture of oil, water and sand -- into the fuel pipeline inside the Sewol.

In a report written on Jan. 28 in 2014, the company reported a similar malfunction, saying the safe operation of the ship was hampered due to the sludge blocking the pipelines. It asked the association again to look into how the sludge-mixed fuel was supplied and who was responsible. But the cause of the problem was not found and the ferry continued to run.

In another paper filed about a week before the disaster, an official from the ferry operator said that he had not discovered “clear” reasons behind the problem even after an on-site inspection.

More than three years after the sinking, little information has been found about the cause, with the bereaved families calling for a full-fledged reinvestigation.

The prosecution concluded in October 2014 that the accident resulted from a combination of the illegal redesign of the ship, overloaded freight and an erroneous sharp turn by an inexperienced crew member. The government’s lax safety regulations were also thought to be a reason.

A special investigative committee was launched in July to examine the salvaged ferry and the cause of the disaster for up to 10 months. The panel is looking into whether there was any mistake by crew members in the steering room and why the ship lost balance during a sudden change of direction.

The 145-meter-long ferry, which had been lying more than 40 meters underwater, was lifted above water in March and moved onto a dry dock at the port of Mokpo in April this year.

The bodies of five victims are still missing, and searches of the ferry’s wreckage and the site of the sinking are underway.

(laeticia.ock@heraldcorp.com)